1. Technical Field
The present invention relates to a progressive power lens having a distance portion for visual recognition of a far working distance, a near portion for visual recognition of a near working distance, and an intermediate portion provided between the distance portion and the near portion, and a design method thereof.
2. Related Art
Eyeglass lenses include progressive power lenses in addition to single focus eyeglass lenses.
As shown in FIG. 7A, as the progressive power lens, there is an aspherical lens having a distance portion 1, a near portion 2, an intermediate portion 3 provided between the distance portion 1 and the near portion 2, and intermediate side portions 4 provided on both sides of the intermediate portion 3.
A principal meridian (main meridian) A is set over the distance portion 1, the progressive portion 3, and the near portion 2. The principal meridian A is provided vertically nearly in the center part in the distance portion 1, provided to be inclined toward the nose side in the intermediate portion 3, and provided to extend vertically in the near portion 2. In the near portion 2, the principal meridian A is deviated toward the nose side by convergence near point at close-range observation.
A part between a start point of progressive power S and a end point of progressive power E of the principal meridian A is a progressive surface on which addition continuously changes. A vertical length between the start point of progressive power S and the end point of progressive power E is a length of progressive zone and a length along the horizontal direction orthogonal to the vertical direction is an amount of inset I.
As shown in FIG. 7B, the power (dioptric power) of the lens on the principal meridian A is a power D1 from the distance portion 1 to the start point of progressive power S, increases from the power D1 to a power D2 from the start point of progressive power S to the end point of progressive power E, and is the power D2 from the end point of progressive power E to the lower part of the near portion 2.
Further, as a design method of a progressive power lens in related art, there are a method of designing a pair of progressive power eyeglass lenses by obtaining an amount of deviation of a sagittal plane, assuming a position of near vision, and shifting meridians from far vision to near vision according to the determined near vision (Patent Document 1 (JP-T-2008-511033), a method of changing a position of a principal meridian located in an intermediate vision distance section and a close vision distance section for designing a progressive power lens in consideration of changes (decreases) of the close vision distance caused with age (Patent Document 2 (JP-A-9-179074)), and further, a method of designing progressive multifocal lens by providing a far vision power measurement position in an upper position of a geometric center of the lens, providing an eye point in the horizontal direction of the geometric center of the lens, providing a near vision power measurement position in a position lower than a geometric center and inner at the nose side of the lens, and providing a principal line of fixation passing through the three positions and dividing the lens into a nose side part and an ear side part (Patent Document 3 (JP-A-8-286156).
In the example shown in FIGS. 7A and 7B, the position of the principal meridian A changes from the start point of progressive power S to the end point of progressive power E by the amount of inset I, and the power of the lens on the principal meridian A is the power D1 from the distance portion 1 to the start point of progressive power S and the power D2 from the end point of progressive power E to the lower part of the near portion 2. The position of the principal meridian A is connected to the start point of progressive power S and the end point of progressive power E as the region of the intermediate portion 3 simply by a straight line, and accordingly, the power of the lens on the principal meridian A only simply changes from the power D1 to the power D2 from the start point of progressive power S to the end point of progressive power E.
That is, in related art, the intermediate portion 3 is not regarded as a region for positive visual recognition, and the amount of inset within the region is not positively considered in the lens design, and there is a problem that feeling of wearing is not satisfactory.
The related art example shown in Patent Document 1 is for setting the optimal meridians (principal meridians) on right and left lenses in consideration of the deviation of the sagittal surface in near vision of a wearer relative to a standard sagittal surface, but not for lens design in consideration of the amount of inset in a region between the far vision region and the near vision region, and thus, the example has the same problem as that of the example in FIGS. 7A and 7B.
The related art example shown in Patent Document 2 is to change the position of the principal meridian located in the intermediate vision distance section and the close vision section, but not in consideration of the intermediate section adjacent to the sections in lens design, and thus, the example has the same problem as that of the example in FIGS. 7A and 7B.
The related art example shown in Patent Document 3 is, for bringing the horizontal arrangement of three points of the far vision power measurement position, the eye point position, and the near vision power measurement position to respond to convergence near point action of eyes for near vision for both right eye and left eye, to locate the eye point position nearer the nose side than the far vision power measurement position and locate the eye point position even nearer the nose side than the near vision power measurement position, and use one curve passing through the three positions as a principal line of fixation. However, the curve is for making the two surface parts divided by the principal line of fixation asymmetric in the horizontal direction with the principal line of fixation in between, but the intermediate region is not focused on. Thus, the example has the same problem as that of the example in FIGS. 7A and 7B.